During a glass container forming process, a metal-oxide coating is typically applied to the exterior of the glass container. Such coatings, may include tin, titanium, or other reactive metallic compounds, or organometallic compounds and may be employed to promote adhesion between the glass and a second protective coating, usually a wax, protecting the glass container from surface damage, such as abrasions and scratches.
The metal-oxide coating is typically applied when the glass container emerges in a heated, fully shaped condition from a glassware forming machine, that is at the “hot end” of the system. The containers are transported away from the forming machine by a conveyor. Temperatures in excess of 400 degrees Centigrade exist at the surface of the glass containers, so that when a heat decomposable inorganic metallic, or organometallic, compound is applied thereto, the compound reacts immediately and is converted to a metal-oxide coating.
It is desirable for the coating to be periodically inspected during the glass forming process. Current quality inspection procedures typically involve an offline process. One or more containers are periodically pulled from the production line, after the container has cooled down to less than about 100 degrees Centigrade (at the “cold end” of the system). The thickness of the metal-oxide coating is then measured to determine whether the thickness is within a thickness tolerance range. If the thickness is outside the tolerance range, all containers produced since the last successful inspection until the production process is corrected may be destroyed. For example, sample containers may be inspected every 4 to 8 hours. If there are about 400 to 500 bottles being formed per minute (or about 25,000 to about 55,000 bottles per hour), a coating deficiency identified after four hours of production may result in a significant loss of inventory.
Various methods exist for detecting defects in objects to be inspected.
U.S. Pat. No. 4,651,568 is directed to a glass bottle inspection method and apparatus that uses an acoustic wave pulse to detect defects.
U.S. Publication No. 2013/0222575 is directed to a glass bottle inspection apparatus and method that detects a defect on the glass bottle by an imaging process via one or plural illuminating units and at least one camera.
U.S. Publication No. 2014/0119634 is directed to a glass bottle inspection method and apparatus that produces differential images from images successively captured from the glass bottle while the bottle is rotated, to determine whether the bottle is defect free.
U.S. Publication No. 2009/0148031 is directed to a surface inspection apparatus which scans the surface of an inspection object with an inspection light, receives reflection light from the surface and generates a two-dimensional image of the object surface based on the reflection light. The apparatus classifies pixels in the two-dimensional image into pixels having tones corresponding to defects on the object surface and pixels having tones not corresponding to the defects.
Various methods exist for determining a coating thickness disposed on objects.
U.S. Publication No. 2004/0065841 is directed to a process and apparatus for testing the coating thickness on a plastic container by shining ultraviolet light through the container to one or more ultraviolet sensors and determining the thickness based on the amount of ultraviolet light passed through the container.
WO 2004/065902 is directed to a method and apparatus for contactless measurement of a coating on a substrate such as a bottle, based on capturing ultraviolet radiation reflected from the substrate.
U.S. Pat. No. 6,252,237 is directed to a method for measuring the thickness of a coating on a coated surface, using a solid state array of light-sensitive elements to measure light emitted from a fluorescing coating composition and measuring the intensity of the coating composition.
U.S. Pat. No. 6,646,752 is directed to a method and apparatus for measuring thicknesses of ultra-thin gate oxide layers, by using heat treatment and ellipsometry.
U.S. Pat. No. 5,208,645 is directed to a method and apparatus for measuring the thickness of a coating around a cylindrical object, by irradiating the object with parallel rays of light in a direction perpendicular to the specimen length and measuring the peak levels of the light intensity of light refracted from the specimen and received via an image detecting device.
U.S. Pat. No. 6,515,293 is directed to a method and apparatus of measuring the thickness of a thin layer formed on a semiconductor wafer by irradiating light onto cells of the wafer and measuring luminance values of light reflected from the wafer.
U.S. Pat. No. 5,991,018 is directed to an apparatus for inspecting a thickness or deteriorating situation of a coating layer using an image pickup unit to receive reflected light or transmission light. The image pickup signal is compared to a reference formula to determine the thickness of the coating. The inspecting apparatus may measure the thickness of the coating layer on the production line.
Current optical thickness measurement methods have difficulty providing accurate measurement of thin coating thicknesses (e.g., less than about 20 nm), as well as accurately identifying small changes in coating thickness, which may provide an indication that the thicknesses are approaching the edge of an acceptable tolerance range (e.g., less than about 5 nm). Accurate determination of the coating thickness at the “hot end” of the system during the in-line production process is also highly desirable, for example, to maintain the coating within the tolerance range and to reduce inventory loss.